1. Field of the Invention
The present invention is generally related to controlling an internal combustion engine, and more particularly, to a method and system for predicting cylinder air charge for a future cylinder event.
2. Background Art
The air-fuel ratio in an internal combustion engine affects both engine emissions and performance. Accordingly, conventional vehicles include systems for controlling the air-fuel ratio in the engine to comply with modern emissions standards, increase fuel economy and improve drivability.
Conventional engine control systems estimate the mass of air entering each cylinder of the engine (referred to as air charge). These conventional systems typically employ a mass airflow (MAF) sensor or manifold absolute pressure (MAP) sensor to generate an input to an air induction model based on manifold filling and volumetric efficiency. Once the mass of charged air entering the cylinder is determined, the systems attempt to match the mass of charged air with an appropriate amount of injected fuel to maintain an optimal air-fuel ratio.
Determining the amount of injected fuel at the time of induction into the cylinder, however, presents several problems. There is typically a time delay between the issuance of a fueling command by the control system and injection of the fuel into a cylinder resulting from physical limitations of the fuel delivery system. This is particularly problematic at high engine speeds and loads where there is less time between engine events. Further, it is desirable to complete fuel injection before the intake valve opens to protect the combustion chamber and to atomize the fuel with the rush of air into the cylinder caused by the initial opening of the intake valve. As a result, estimation of air charge concurrent with actual induction of air into the cylinder occurs too late in the combustion process.
Several systems and methods have been developed that predict the air charge for future cylinder events. For example, in SAE 2000-01-0258, Allen J. Kotwicki et al., xe2x80x9cAn Algorithm to Compensate for Air Charge Prediction Errors,xe2x80x9d SAE 2000 World Congress, Detroit, Mich., Mar. 6-9 2000, a method is disclosed for determining the cylinder air charge for a future cylinder event using a signal from a mass air flow (MAF) sensor. Commonly assigned U.S. Pat. No. 6,170,475 B1, the entire disclosure of which is incorporated herein by reference, discloses a system and method for determining the cylinder air charge one or more cylinder events into the future for an engine having a conventional mechanically controlled throttle plate and a manifold absolute pressure (MAP) sensor. These systems and methods, however, still suffer from a relatively high level of uncertainty in their air charge predictions.
The inventors herein have recognized a need for a method and system for controlling an engine that will minimize and/or eliminate one or more of the above-identified deficiencies.
The present invention provides a method and a system for predicting cylinder air charge in an internal combustion engine for a future cylinder event.
A method in accordance with the present invention includes the steps of calculating a pressure in an intake manifold of the engine and estimating a position for an electronically controlled throttle plate of the engine at least one cylinder event in the future in response to a command from an electronic throttle control. The method also includes the step of estimating the rate of change of pressure in the intake manifold responsive to the previously measured intake manifold pressure and the estimated position of the electronically controlled throttle plate. Finally, the method includes the step of calculating the cylinder air charge for the future cylinder event responsive to the rate of change of pressure in the intake manifold.
A system in accordance with the present invention includes an electronic control unit that is configured to calculate a pressure in the intake manifold of the engine and estimate a position of the throttle plate of the engine at least one cylinder event in the future responsive to an electronic throttle control command. The electronic control unit is further configured to estimate the rate of change of pressure in the intake manifold responsive to the previously measured intake manifold pressure and the estimated position of the electronically controlled throttle plate. Finally, the electronic control unit is configured to calculate the cylinder air charge for the future cylinder event responsive to the rate of change of pressure in the intake manifold.
The present invention represents an improvement as compared to conventional systems and method for predicting cylinder air charge for future cylinder events. The inventive system and method use the delay between an electronic throttle control (ETC) command and actual throttle positioning responsive to the command to better anticipate the air flow at a cylinder intake port during a future cylinder event. In this manner, the inventive system and method reduce the uncertainty found in conventional systems and methods. Further, the inventive system and method predict future air charge without the use of a manifold absolute pressure sensor.